Technical Service Center — Water Conveyance Group
The Bureau of Reclamation designs tunnels to provide various functions. These functions can be:
- Conveying water over long distances.
- Allowing passage of automobiles and trucks.
- Working around dams and powerhouses associated with dams.
- Providing passage underground for various other reasons.
Reclamation engineers maintain a database of water conveyance tunnels. The database also contains information on some other tunnels.
Tunnel construction begins by excavating the ground. Tunnelers excavate tunnels using various methods including:
- Tunnel Boring Machines (TBM)
- Drill and Blast
- Hand excavation
Material that is being excavated must be removed from the tunnel. TBM's use conveyor belts to transport the waste material away from the heading to a second conveyor belt or muck train. Drill and blast operations many times use load-haul-dump (LHD) machines to transport the waste material from the heading to the waste pile outside the tunnel.
The excavated hole must remain open as excavation at the heading progresses. If the ground cannot support itself until final support is installed then miners must install initial support. The tunnel can be initially supported by various methods. The most common are:
- Structural steel tunnel supports commonly called steel supports. Steel supports usually remain the same shape throughout the tunnel except at the portal where they sometimes change shape.
- Rock bolts.
- Liner plate.
If the excavated opening cannot remain open for the life of the tunnel than the opening is permanently held open using final support. Concrete linings are usually used for final support. Tunnelers do this by using concrete forms on the inside face and pumping concrete into the space between the concrete forms and rock
Sometimes these are the same supports, for example:
- Precast concrete segmental liners.
- Rock bolts and rock anchors that are permanently protected from corrosion.
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